1. Field of the Invention
This invention relates to sound technology in general and, in particular, relates to a speaker having a single driver element and multiple apertures in an array.
2. Description of the Related Art
Speakers convert electrical signals to sound waves that allow listeners to enjoy amplified sounds. One of the factors that determine the quality of the speaker-generated sound heard by the listener is the sound pressure level (SPL). The quality of the SPL generally depends, among other factors, on the size of the speaker relative to the distance between the speaker and the listener. Generally, a larger distance requires a larger speaker size. Obviously, there is a practical limit on how large a speaker can be made. For example, an overly large speaker may create difficulties in transporting or mounting. Furthermore, a correspondingly large driving element needed to drive such a large speaker may require an impractical amount of power.
To circumvent such drawbacks, an array of smaller sized speakers can be used to achieve similar acoustic results. As is generally understood, sound waves from the individual smaller speakers may combine to yield a combined sound wave that behaves similar to that emanating from a single large speaker.
Effective and coherent combination of sound waves may be achieved when certain wave related parameters are satisfied. One such requirement is that the individual waves emanating from the smaller speakers need to have a substantially fixed phase difference among themselves. When all of the smaller speakers in a linear arrangement are driven substantially in phase (substantially zero phase difference), a resulting combined wave propagates in a direction normal to a line defined by the speakers. A substantially fixed non-zero phase difference among the individual waves results in a combined wave that propagates at an angle with respect to the normal direction. In typical arrayed speaker applications, the individual smaller speakers are driven substantially in phase.
Another requirement for a quality combined wave from the array of smaller speakers is that the spacing between the speakers need to have certain dimension relative to the wavelength of the sound waves. As a rule of thumb, it is generally accepted that the spacing between two neighboring speakers needs to be smaller than the wavelength of the sound wave in question. In some standards, the spacing requirement is tighter at half the wavelength. One reasons is that if the spacing is larger than the wavelength (or half the wavelength), the resulting combination of the waves suffers from poor directional properties, including unwanted side lobes of sound patterns away from the desired direction.
The wavelength of a wave is determined as wave velocity divided by wave frequency. The wave velocity of sound in room temperature air is approximately 1130 ft/sec. For an exemplary low frequency audio sound having a frequency of 200 Hz, the corresponding wavelength is approximately 68″. Similarly, a midrange audio sound with a frequency of 2000 Hz, the corresponding wavelength is approximately 6.8″ For the low frequency audio sound, maintaining the spacing between the speakers less than the wavelengths under the exemplary 68″ is easily achieved. For the midrange audio sound, arranging the midrange speakers with spacing under the exemplary 6.8″, while more challenging than that of the low frequency case, is still achievable.
For a high frequency audio sound with an exemplary frequency of 20000 Hz, the corresponding wavelength is approximately 0.68″. This relatively small wavelength poses a problem for spacing of the high frequency speakers, since the components of the speaker has physical limitations on how small they can be made. For example, the magnet assembly that drives the speaker cone needs to be of certain minimum size such that positioning two such speakers adjacent to each other yields a center-to-center spacing larger than the exemplary wavelength of 0.68″. Thus, the resulting high frequency sound emitted from such an array of high frequency speakers suffers from the aforementioned directionality problems.
For the foregoing reasons, there is a continuing need for an improved system and method for transmitting a sound wave from a speaker or a plurality of speakers. In particular, there is a need for transmitting high frequency sound waves in a manner that allows increasing of the dimension of the transmitted wavefronts while mitigating the undesired effects that degrade the sound quality.